The disclosed invention relates to refrigerant hoses for use in automotive and industrial air conditioners.
The automotive industry uses hoses for transporting refrigerants. The hoses generally have a three-layer laminar construction consisting of an innermost layer, an outermost cover layer located radially outwardly of the inner tube, and a reinforcing fiber layer interposed between the innermost layer and the outermost layer. Generally, the inner and outer layers are formed of rubber. The reinforcing fiber layer usually is a mesh structure formed by braided organic yarn such as polyester fiber, rayon fiber, or nylon fiber. The outer cover typically is formed of ethylene propylene diene rubber (EPDM) or chloroprene rubber (CR). Adhesion layers be may employed between the layers.
The known multi-layered rubber hoses discussed above have a high degree of flexibility. Because of this property of the rubber materials, rubber hoses can be handled with ease. However, rubber materials generally tend to have high gas permeability. Attempt to improve resistance of conventional rubber hoses to refrigerant permeation by incorporating polyamide layers such as nylon 6 or nylon 66 as an inner layer.
The nylons used for inner hose layers are conventionally plasticized polyamides. Plasticizer is added to the polyamide to improve the flexibility of the material; flexibility being a necessary characteristic of the hose. However, the addition of plasticizer decreases the permeability characteristics of the nylon; also a necessary characteristic of the hose. To achieve an acceptable compromise of the required characteristics, the thickness of the nylon inner core layer is conventionally at least 0.5 mm, see U.S. Pat. No. 4,633,912 who discloses a polyamide blend cores tube with a gauge thickness of 1.07 mm and 0.81 mm.
The present invention is directed to a hose that is particularly useful for transporting refrigerants. The hose has a high resistance to permeation and high flexibility.
The inventive hose has a selection of two different polyamides to form the inner core layer of a hose. The inner core layer is formed from co-extruded nylon layers. The inner core layer is formed from a polyamide that is nonplasticized, flexible, and has moderate resistant to refrigerant permeation. The outer core is formed from a polyamide that is nonplasticized, less flexible than the inner core polyamide, and has a higher resistant to refrigerant than the inner core polyamide. The combination of the two layers and the selective thickness of the two core layers provide the needed flexibility, heat resistance, and high resistance to refrigerant permeation.